Inclined hearth kiln for the firing and sintering of material

ABSTRACT

An inclined burning and sintering kiln has a combustion chamber having a combined inlet and preheating shaft terminating, at the level of a roof of the chamber, above the upper end of a sloping operative surface of the chamber. A partition extending across the chamber below the lower edge of the inlet shaft wall which adjoins the roof, and thus below the level of the inside of the roof, reduces the thickness of the build-up layer on the operative surface of material passing into the chamber via said inlet shaft, over said operative surface to a discharge shaft at the bottom of the chamber, and thus renders more efficient the treatment of the material.

United States Patent 1 [111 3,765,827 Beckenbach Oct. 16, 1973 INCLINED HEARTH KILN FOR THE 3,164,380 1/1965 Kus 432/100 FIRING AND SINTERING OF MATERIAL [76] Inventor: Karl Beckenbach, l-lildegundisallee 33, Buderich B/Dusseldorf, Meererbusch, Germany [22] Filed: July 24, 1972 [21] Appl. No.: 274,237

[30] Foreign Application Priority Data July 28, 1971 Germany P 21 37 723.1

[52] US. Cl. 432/95 [51] Int. Cl. F27b 1/00 [58] Field of Search 432/95, 101, 100

[56] References Cited UNITED STATES PATENTS 238,455 3/1881 Stetefeldt 432/]01 Primary Examiner-John J. Camby Att0rney-l-lill, Sherman, Meroni, Gross & Simpson ABSTRACT An inclined burning and sintering kiln has a combustion chamber having a combined inlet and preheating shaft terminating, at the level of a roof of the chamber, above the upper end of a sloping operative surface of the chamber. A partition extending across the chamber below the lower edge of the inlet shaft wall which adjoins the roof, and thus below the level of the inside of the roof, reduces the thickness of the buildup layer on the operative surface of material passing into the chamber via said inlet shaft, over said operative surface to a discharge shaft at the bottom of the chamber, and thus renders more efficient the treatment of the material.

5 Claims, 5 Drawing Figures INCLINED HEARTH KILN FOR THE FIRING AND SINTERING OF MATERIAL The invention relates to a burning and sintering kiln, of use for example for limestone or the like. Burning and sintering kilns are known of a type having one combustion chamber or a number of combustion chambers which are disposed one above another and each of which combustion chambers comprises a substantially horizontal curved arch forming the roof of the chamber, a sloping operative surface with lateral boundaries, a vertical combustion chamber wall opposite said sloping surface, burners in the top of the vertical wall, a substantially vertical preheating shaft extending into the top of the combustion chamber over the upper end of the sloping operative surface, and a discharge shaft at the lower end of the sloping operative surface.

The angle of slope of the operative surface with respect to the horizontal must, in kilns of this kind, be greater than the angle of repose of the material sliding down over the operative surface, to ensure that the dust which trickles through the descending layer can also slip down over the operative surface. Consequently, the thickness of the layer of material sliding down and operative surface increases downwardly, and so the depth to which gases and radiated heat can penetrate into the layer decreases downwardly, in relative terms.

Even in cases where a number of such combustion chambers are disposed one above the other so that the discharge shaft of one communicates with the preheata first vertical combustion chamber wall, burner means in said first vertical combustion chamber wall adjacent the top thereof, a substantially horizontal arched top wall having opposite ends connected at one said end to the top of said vertical wall, a first substantially vertical preheating shaft wall connected at its lower end to the other said end of said top wall a second substantially vertical preheating shaft wall spaced from the said first vertical preheating shaft wall, a fourth vertical wall adjacent and spaced from the lower end of the first said ing shaft of the next and so on, non-uniform and inadequate heating of the material in the top of the top combustion chamber due to excessive layer thickness is not compensated for adequately by relayering of the material in the lower combustion chamber or chambers as it moves along its path. It is not practicable to reduce the width of the preheating shaft in order to reduce the layer thickness adequately in the bottom part of the combustion chamber since the reduction in shaft crosssection which would be needed for this purpose would introduce the risk of jamming occurring at the top of the operative surface in the top combustion chamber and, more particularly, near the exit end of the preheating shaft, for initial heating of the material in the preheating zone leads, more particularly with limestone or dolomite, to heat expansion of the material. The volume of the discrete lumps starts to decrease only when the carbon dioxide contents start to evolve. If the crosssectional narrowing is therefore operative as early as the preheating zone, there is a risk of jamming, the jamming clearing only when carbon dioxide starts to evolve.

Another disadvantage of having a very thick layer on the operative surface is that it reduces the internal volume of the combustion chamber, but for complete combustion of the fuel charges and to ensure that the combustion material is not treated harshly, it is very important for there to be sufficient free space above the layer of material in the combustion chamber or for there to be an adequate spacing between the surface of the material and the operative surface.

It is an object of the invention to provide an improved kiln in which the above disadvantages are avoided.

According to the invention there is provided an inclined burning and sintering kiln comprising means defining at least one combustion chamber and including vertical combustion chamber wall and a sloping wall connecting the lower end of said second vertical preheating shaft wall and the upper end of said fourth vertical wall, said sloping wall defining a sloping operative surface opposed to said first mentioned vertical wall, and opposed side walls connecting said first vertical combustion chamber wall said top wall and said sloping wall to define the combustion chamber and connecting said first and second preheating shaft wall to define a substantially vertical preheating shaft connected at its lower end to the top of the combustion chamber, said side walls also connecting said fourth vertical wall and said first vertical combustion chamber wall to define therewith a discharge shaft extending downwards from the bottom of the combustion chamber, said sloping operative surface sloping downwardly towards said first vertical combustion chamber wall from the preheating shaft to the discharge shaft, said kiln further including at least one support wall extending vertically upwards from said sloping operative surface and parallel with said side walls and at least one partition supported by said support wall in the region below said first preheating shaft wall and extending between said opposed side walls, said partition having a lower edge spaced from said sloping operative surface whereby granular material supplied through said preheating shaftwill be constrained to pass into said combustion chamber only under the lower edge of said partition.

The partition brings about a reduction in thickness of the material treated in the kiln over said sloping surface, with simultaneous improvement in combustion conditions, leading to more uniform heating of the material in the combustion chamber.

The presence of the partition borne by one or more support walls also helps to even out the rate of descent of the material transversely of the operative surface. In kilns devoid of bearing walls the rate of descent is decreased considerably in the two lateral zones of the operative surface, i.e. adjacent the chamber side walls, as compared with the central zone thereof, due to friction between the material and the two side walls of the combustion chamber, whereas the presence of one or more support walls parallel with the side walls and disposed therebetween leads to a more uniform rate of descent in all parts of the combustion chamber by, subdividing the operative surface into zones each of which is flanked by walls, the two outer zones being each disposed between a respective combustion chamber side wall and a supporting wall and, if there is more than one bearing wall, the or each central zone of the operative surface being disposed between two bearing walls.

Furthermore, in prior inclined burning and sintering kilns of the general type to which the invention relates, the combustion chamber roof or top wall is generally arched, (i.e. vaulted) for reasons of strength and for this reason, in prior kilns more material issues from the bottom of the preheating shaft near the centre of the arch thenadjacent the side walls of the chambers, i.e. more material issues over the central part of the sloping operative surface than adjacent the sides thereof, so that the thickness of the layer of material on said operative surface is greater in the central zone than in the side zones.

In a kiln according to the invention it is possible to shape the lower edge of the partition independently of the shape of the top wall of the combustion chamber so that it is possible to shape the partitions lower edge so as to ensure a layer of material which is even over the width of the operative surface.

This feature is of advantage more particularly in large inclined kilns in which the arch height of the vaulting is correspondingly large and in which, in the absence of partition, the layer thickness in the central region would be very much greater than it is at the sides of the operative surface. The means previously needed in such large kilns to compensate for differences, in the thickness of the layer of material and in the speed of descent, over the width of the operative surface, such as special control of the burners allocated to the various zones, can thus be omitted in kilns according to the present invention.

Embodiments of the invention are described hereinafter with reference to the accompanying drawings wherein:

FIG. 1 is a central longitudinal section through the top combustion chamber of one embodiment of inclined kiln according to the invention;

FIG. 2 is a secton on the line 22 of FIG. 1, looking in the direction of the corresponding arrows;

FIG. 3 is a section on the line 33 of FIG. 1; looking the direction of the corresponding arrows;

FIG. 4 is a view' similar to FIG. 1 of another embodiment of inclined kiln, and

FIG. 5 is a section on the line 5-5 of FIG. 4, looking in the direction of the corresponding arrows.

The drawings show the top combustion chamber only of a dual inclined kiln comprising two combustion chambers which are disposed one above the other.

As can be seen in FIG. 1 the combustion chamber 10 includes a top wall or roof 14 which is generally horizontal in longitudinal section. One end of the top wall 14 terminates at and is connected with the upper end of a vertical combustion chamber wall 20. The opposite end of the top wall 14 terminates at and is connected to the lower end of a first vertical wall of a preheating shaft extending upwardly from the level of the top wall 14. Spaced from and parallel with the first vertical preheating shaft wall on the side thereof furthest from the wall 20 is a second vertical preheating shaft wall, the distance between said preheating shaft walls being substantially less than the length of the top wall 14 between the wall 20 and the first preheating shaft wall. At the lower end of the combustion chamber is a fourth vertical wall parallel with the wall 20 and spaced therefrom on the same side of the wall 20 as the preheating shaft, at the same distance as the spacing between said preheating shaft walls. A sloping wall defining a sloping operative surface 16 extends from the top of said fourth vertical wall to the bottom of said second preheating shaft wall. The walls shown in cross-section in FIG. 4 are connected by two parallel spaced vertical side walls so that the combustion chamber proper is defined between the top wall 14, wall 20, the wall providing the surface 16 and said two side walls whereas there is defined between said side walls and said first and second preheating shaft walls a preheating shaft 12 extending upwardly from the top of the chamber and between said two side walls, the wall 20 and said fourth vertical walls a discharge shaft 24 at the bottom of the chamher.

As can be seen in FIG. 2 the top wall 14 is arched transversely to provide structural strength. The lower end of said second preheating shaft wall within the chamber is at substantially the same level as the ends of the arch of the top wall. Burners 18 are provided in the wall 20 adjacent the top thereof.

It will be noted that the preheating shaft 12 and discharge shaft 24 are parallel but offset with respect to each other. The lower combustion chamber (not shown) may be identical with the upper combustion chamber 10 in all respects (including those yet to be described), but is effectively displaced through about a vertical axis with respect to the upper chamber, the preheating shaft of the lower chamber being formed as a continuation of the discharge shaft 24 of the upper chamber so that the lower end of the wall 20 forms the second preheating shaft wall of the lower chamber and said fourth vertical wall forms the first preheating shaft wall of the lower chamber so that the discharge shaft of the lower chamber is aligned with the preheating shaft of the upper chamber, and the operative surfaces of the two chambers slope in opposite directions. Clearly a series of identical chambers may be disposed one above the other in this fashion, disposed alternately in the same fashion. Thus the material introduced into the upper chamber via the preheating shaft thereof descends along the operative surface thereof to the discharge shaft and thence to the lower chamber and so on.

The slope angle of the surface 16 is greater than the angle of repose of the material entering through the feed shaft 12. If there were no other constructional elements in the chamber 10 than those already described, so that the chamber was of substantially conventional construction, the material entering through the shaft 12 would take up a position on the operative surface 16 such that there would be a continuous'increase downwardly in the thickness of the layer of material on the surface 16. The position which the surface of this layer would occupy is indicated in FIG. 1 by the build-up line a extending from the shaft 12 to the vertical combustion chamber wall 20. Consequently, at the bottom of the combustion chamber of conventional inclined kilns the thickness of the layer of material is so great that the combustion gases from the burners cannot fully penetrate the layer, nor can the heat radiating from the unoccupied part of the combustion chamber. Also, the reduction of the available gas flow space in the combustion chamber due to the thickness of the layer inhibits proper combustion of the liquid or gas fuel.

In the embodiment of FIG. 1, to reduce the thickness of the layer of material in the combustion chamber, a relatively narrow partition 26 is provided the upper edge of which is spaced a short distance away from the arched roof I4 and the lower edge of which is spaced substantially from the surface 16. The partition extends transversely from one wall 22 to the other, i.e. entirely across the chamber and is disposed generally below the lower edge of said first wall of shaft 12 i.e., the wall which merges with the arch. The partition 26,is anchored at its ends in the side walls 22 and is supported intermediate its ends by two support walls 28 which extend vertically parallel with the side walls, from the surface 16 upwardly to the partition. The walls 28 are thinner than the walls 22.

As can be gathered from FIGS. 1 to 3, the partition 26 is arcuate and substantially follows the contour of the arch 14.

The partition 26 comprises three small arches, one extending between one wall 22 and the adjacent wall 28, one extending between the two walls 28, and the remaining one extending between the other wall 22 and the adjacent wall 28. In the embodiment of FIGS. 1 to 3 the side faces of the partition 26 slope downwardly towards the surface 26 at an acute angle with respect thereto. It will be evident from FIG. 3 that the portions of the partitions between adjacent walls 28 or adjacent walls 22 and 28 are also arcuate when viewed from above in a direction parallel to their side surfaces. This renders these portions better able to withstand pressure exerted thereon by material issuing from shaft 12.

When the partition 26 is provided, the material builds up below the partition along a line b, (indicating the upper surface of the layer) which is a much lower line than the line a, with the result that the thickness of the layer is decreased considerably and the unoccupied volume of the combustion chamber is increased correspondingly.

Preferably, each bearing wall 28 has its edge nearest the wall extending from a position near the lower end of the surface 16 vertically upwards to the neighbourhood of the partition 26, on the side of the latter nearer the wall 20, and has an edge extending from the upper edge of partition 26, horizontally as far as the plane of the inner face of said first wall of the shaft 12, to meet a further edge which slopes downwards to the operative surface 16 in a direction away from the wall 20 and at an acute angle to surface 16.

In the embodiment shown in FIGS. 1 to 3, in which there is a relatively narrow gas flow passage extending over the whole width of the kiln between the top edge of the partition 26 and the top wall 14, the walls 28 can, if preferred, be extended right up to the top wall 14 to support the latter. 7

The embodiment of FIGS. 4 and 5 is similar to that of FIGS. 1 to 3, except that the partition 26 has its side faces flat and vertical, its side face remote from the vertical chamber wall bearing the burners being in the plane of the inner face of the first wall of the preheating shaft, and the top of the partition 26 extends right up. to the top wall to provide additional support for the latter. The top wall of the chamber can be formed in a single arch as indicated by the upper edge of the solid black area in FIG. 5, or the top wall can be formed in three individual vaults or arches as shown below the solid black area in FIG. 5.

It will be appreciated that three small individual arches formed in this fashion are stronger and more reliable than a single arch of the same general contour. As a variant the top wall proper may be formed as a single arch or vault and simply the lower end of the first vertical wall of the preheating shaft formed in three small arches.

No gas flow passage at all need be left in the embodiment of FIGS. 4 and 5, between the partition and the closure vault of the preheating shaft, the entire flow of combustion gases going downwardly, around the partition. An advantage of this feature is that the combus- 6 tion chamber can be made much wider by the use of three vaults instead of only one as previously; the large free area of the combustion chamber which is important for combustion is retained.

The burners 18 are so disposed as to be opposite the combustion chamber portions bounded laterally by the two bearing walls or by one bearing wall and one side wall 24. In the embodiment shown, therefore, there are three burners.

While in the embodiments described with reference to the drawings there are two supporting walls 28 which are spaced equally from each other and from the adjacent side walls 22 it will be appreciated that in certain cases a single supporting wall 28 disposed midway between the walls 22 may be adequate, while it is possible, particularly in constructions such as shown in FIGS. 4 and 5 in which the partition serves also to support the top wall, to employ three or more walls 28, particularly when very wide chambers with multiple vaulted roofs are contemplated.

Furthermore while, in the embodiments shown in the drawings, the lower edge of the partition is arched to the same extent as, or even more severely than, the top wall it is possible to form the lower edge of the partition either straight and parallel with the surface 16 or as a series of small arches each extending between two walls 28 or 26, 28 the series extending generally in such a straight line. By this expedient the thickness of the material layer on the surface 16, in different zones transversely thereof, may be maintained substantially equal.

I claim:

1. An inclined burning and sintering kiln comprising means defining at least one combustion chamber and including a first vertical combustion chamber wall, burner means in said first vertical combustion chamber wall adjacent the top thereof, a substantially horizontal arched top wall having opposite ends connected at one said end to the top of said vertical wall, a first substantially vertical preheating shaft wall connected at its lower end to the other said end of said top wall, a second substantially vertical preheating shaft wall spaced from the said first vertical preheating shaft wall, a fourth vertical wall adjacent and spaced from the lower end of the first said vertical combustion chamber wall and a sloping wall connecting the lower end of said second vertical preheating shaft wall and the upper end of I said fourth vertical wall, said sloping wall defining a sloping operative surface opposed to said first mentioned vertical wall, and opposed side walls connecting said first vertical combustion chamber wall, said top wall and said sloping wall to define the combustion chamber and connecting said first and second preheating shaft wall to define a substantially vertical preheating shaft connected at its lower end to the top of the combustion chamber, said side walls also connecting said fourth vertical wall and said first vertical combustion chamber wall to define therewith a discharge shaft extending downwards from the bottom of the combustion chamber, said sloping operative surface sloping downwardly towards said first vertical combustion chamber wall from the preheating shaft to the discharge shaft, said kiln further including at least one support wall extending vertically upwards from said sloping operative surface and parallel with said side walls and at least one partition supported by said support wall in the region below said first preheating shaft wall and extending between said opposed side walls,

said partition having a lower edge spaced from said sloping operative surface whereby granular material supplied through said preheating shaft will be constrained to pass into said combustion chamber only under the lower edge of said partition.

2. The kiln of claim 1 wherein the or each said supporting wall has a first edge which extends substantially vertically from adjacent the lower end of said sloping operative surface to the level of said partition on the side of said partition nearer said first vertical combustion chamber wall and has a further edge which slopes downwardly away from said first vertical combustion chamber wall to said sloping operative surface from a vide additional support for said top wall. 

1. An inclined burning and sintering kiln comprising means defining at least one combustion chamber and including a first vertical combustion chamber wall, burner means in said first vertical combustion chamber wall adjacent the top thereof, a substantially horizontal arched top wall having opposite ends connected at one said end to the top of said vertical wall, a first substantially vertical preheating shaft wall connected at its lower end to the other said end of said top wall, a second substantially vertical preheating shaft wall spaced from the said first vertical preheating shaft wall, a fourth vertical wall adjacent and spaced from the lower end of the first said vertical combustion chamber wall and a sloping wall connecting the lower end of said second vertical preheating shaft wall and the upper end of said fourth vertical wall, said sloping wall defining a sloping operative surface opposed to said first mentioned vertical wall, and opposed side walls connecting said first vertical combustion chamber wall, said top wall and said sloping wall to define the combustion chamber and connecting said first and second preheating shaft wall to define a substantially vertical preheating shaft connected at its lower end to the top of the combustion chamber, said side walls also connecting said fourth vertical wall and said first vertical combustion chamber wall to define therewith a discharge shaft extending downwards from the bottom of the combustion chamber, said sloping operative surface sloping downwardly towards said first vertical combustion chamber wall from the preheating shaft to the discharge shaft, said kiln further including at least one support wall extending vertically upwards from said sloping operative surface and parallel with said side walls and at least one partition supported by said support wall in the region below said first preheating shaft wall and extending between said opposed side walls, said partition having a lower edge spaced from said sloping operative surface whereby granular material supplied through said preheating shaft will be constrained to pass into said combustion chamber only under the lower edge of said partition.
 2. The kiln of claim 1 wherein the or each said supporting wall has a first edge which extends substantially vertically from adjacent the lower end of said sloping operative surface to the level of said partition on the side of said partition nearer said first vertical combustion chamber wall and has a further edge which slopes downwardly away from said first vertical combustion chamber wall to said sloping operative surface from a position closely adjacent the lower end of said first preheating shaft wall on the other side of said partition.
 3. The kiln of claim 1 wherein said partition has an upper edge spaced a short distance below said arched top wall.
 4. The kiln of claim 1 wherein said partition has an upper edge which is arched to correspond generally to the arching of said top wall.
 5. The kiln of claim 1 wherein said partition is connected at its upper edge to said arched top wall to provide additional support for said top wall. 